Construction of a large number of structures, including buildings, sewer lines, prefabricated structures, etc., begins with the placement of a stone base. In some instances, the stone base must be accurately placed and graded for the proper construction of the structure. For example, a gravity sewer line is constructed at a sloped grade under which the stone base is graded at that same slope to provide proper support for the sewer line. Another example of a stone base that requires precise grading is the stone base under a pre-cast concrete wall.
A pre-cast concrete wall is manufactured at a remote site and shipped to the job site to be erected. A pre-cast concrete wall, constructed as disclosed, for example, in U.S. Pat. No. 7,530,203, granted on May 12, 2009, to Robert W. Hare, et al., is formed with a footer beam that is placed on a graded stone base. A plurality of the pre-cast concrete wall panels are placed around the pre-graded stone base to form an enclosed foundation for a building to be subsequently built on the foundation. The proper support of the footer beams requires that the stone base beneath the pre-cast concrete walls is graded level in both longitudinal and transverse directions so that the stone will contact the underside of the footer beam all along the erected foundation.
Conventionally, the grading of the stone base is first rough graded to within about an inch of being level around the location for the erection of the pre-cast concrete walls. Final grading is accomplished by first setting grading monuments, such as a piece of a wooden two by four placed into the stone base, around the perimeter of the foundation to be erected and then leveled at the desired elevation by a laser level. The stone base can then be hand graded by sliding a screed between consecutive monuments so that the stone base between the monuments is at the same elevation as the adjacent monuments. This process is repeated around the perimeter of the foundation until the entire area on which the pre-cast concrete walls are to be erected is leveled at the desired grade elevation. This process is extremely time consuming and labor intensive.
Accordingly, it would be desirable to provide an apparatus that would be operable to grade a stone base accurately and uniformly without requiring the setting of elevation monuments and hand screeding to accomplish the graded stone base.